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A Amorim

Publications and source records attributed to A Amorim.

At least 73 records · Page 4Linked to original sources
PubMed1999

Segregation analysis of tetra- and pentanucleotide short tandem repeat polymorphisms: deviation from Mendelian expectations.

Short tandem repeat (STR) polymorphisms are powerful tools for linkage studies, chromosome mapping and population analysis. The instability of these microsatellite regions is a prevailing event in several tumors and human genetic diseases and, despite various reports associating instability-related genes and meiosis control, the dynamics of these STR regions in normal cells/individuals has frequently been disregarded. Having previously assayed somatic instability in gastric cancer for some tetra- and pentanucleotide STRs and given the increased application of this type of marker for routine forensic expertise, we report the results of an extensive analysis of segregation in nuclear families of a normal population for the same loci. No mutations were detected in 2374 parent/offspring allelic transfers at TH01, TPO, VWA31/A, MBPB, and CD4 STR loci. Nonsignificant differences were found between gene frequencies of parental and offspring generations. However, the segregation analysis revealed significant deviation from Mendelian expectations for: VWA31/A locus - alleles 19, 17 and 14 and TH01 locus - allele 6. In particular, parental meiosis strongly favored specific allele transmission, depending upon the sex of the offspring. Specific mating types are apparently responsible for most of these abnormal segregations. These results suggest selective factors working either at the gametic or zygotic levels.

Female↗
PubMed1999

Detection of additional structural variation at the FES/FPS system and population data from S. Tomé e Príncipe and North Portugal.

Comparative analysis of heteroduplex patterns on the STR FES/FPS system led to the detection of a new non-consensus allele 10 in the African population of São Tomé e Príncipe. Automated sequencing confirmed a T-->C substitution at position 177 (1stT of the 6th repeat) which was exclusively found in haplotypic combination with base A in the previously described polymorphic position 34. The new substitution was not detected in a sample from North Portugal. Sequence analysis revealed a triplet of inverted bases, from positions 101 to 103, relative to the sequence described in the GeneBank (Accession No. X06292). This work confirms the capacity of heteroduplex analysis in the detection of DNA structural microvariation and emphasises the complementary utility of manual system analysis and semi-automated techniques for a full characterisation of the genetic variability of STRs.

Adult↗
PubMed1999

Dynamics of microcystins in the mussel Mytilus galloprovincialis.

The accumulation and depuration of hepatotoxins produced by the freshwater cyanobacterium Microcystis aeruginosa in the mussel Mytilus galloprovincialis was studied. Mussels were fed daily 10(5) cells/ml of the toxic cyanobacterium that produces microcystin-LR (MCYST-LR), for four days. After that period animals were placed in toxin free water and were fed the diatom Nitzschia sp. During two weeks the concentration of the toxin in the mussels, as also in their feces and in the water where animals were placed individually during 24 h, were monitored using an ELISA assay. No mussel mortality was registered during the whole experiment. Mussels showed a maximum detectable level of MCYST of 10.7 microg/g mussels dry weight (DW) during the accumulation period, rising to 16.0 microg MCYST/g mussel DW by day two of the depuration period. Then there was a decrease trend with peaks of toxin at days 6, 8, 11 and 14. The rise of the toxin level on day two of the depuration period seems to have been due to the reingestion of contaminated feces. In fact, feces showed high amounts of MCYST during the first days of depuration with a maximum of 140 microg/d DW on day 3. This coincided with a 50% decrease on the detectable toxin in the mussels reflecting the emptiness of their digestive tract. In the water the highest level of the toxin was 2.5 microg MCYST/liter and some toxin peaks were also observed during the depuration period. This fluctuation of the toxin levels in the mussels, feces and water may be related to the renewal of protein phosphatases and subsequent release of unbound toxins. Results show that depuration of MCYST by mussels is not a very rapid process and contamination by feces containing MCYST is likely to occur and increase the persistence of these toxins in the mussels after the bloom disappearance. Monitoring programs for harmful algal blooms usually include only toxic dinoflagellates and diatoms and their toxins in bivalves. Taken into account the present work they should also include hepatotoxins from cyanobacteria, namely in brackish waters such as estuaries of eutrophic rivers in order to avoid human health hazard.

Animals↗
PubMed1999

MUC1 gene polymorphism does not explain the different incidence of gastric cancer in Portugal and Denmark.

MUC1 is a highly polymorphic mucin type glycoprotein expressed on the surface of many epithelia, including gastric mucosa, and is present in several body fluids and mucous secretions. A genetic polymorphism due to variation in length of a 60 bp tandemly repeated sequence domain constitutes more than half of the coding region of the glycoprotein. We demonstrated previously in a Portuguese population sample that the frequency of small MUC1 alleles is increased in patients with gastric carcinoma, suggesting that the possession of small MUC1 alleles confers increased risk for gastric carcinoma development. This finding raised the possibility that the very high prevalence of gastric carcinoma in Portugal could be partly due to a high frequency of small MUC1 alleles in the Portuguese population. In the present study we compared the MUC1 allele distribution in a population of Danish blood donors with the distribution in a population of Portuguese blood donors. The frequency of small MUC1 alleles was significantly higher in the Danish than in the Portuguese sample, thus failing to lend support to the hypothesis that a relatively higher frequency of the small MUC1 alleles might account for the high prevalence of gastric carcinoma in Portugal when compared to Denmark.

Adult↗
PubMed1999

Thiopurine methyltransferase pharmacogenetics: alternative molecular diagnosis and preliminary data from Northern Portugal.

The thiopurine methyltransferase (TPMT) genetic polymorphism has been shown to have a highly significant clinical impact, namely in the therapeutic efficiency of thiopurine drugs used in the treatment of a wide range of diseases. Available diagnostic methods, although reproducible and sensitive, are relatively laborious. Thus population studies are still very scarce. In this work we describe a new polymerase chain reaction-single strand confirmational analysis based protocol for TPMT specific detection which introduces a substantial technical simplification avoiding the use of restriction enzyme treatment after polymerase chain reaction amplification. Additionally, the use of this protocol allows the simultaneous detection of a T474 to C substitution, a frequent silent mutation in the North Portuguese population (TPMT*1S = 0.215). In a sample of 310 unrelated Northern Portuguese individuals, 15 were found to be heterozygous for the TPMT*3A allele (defined by the presence of two transitions, G460 to A and A719 to G) which is associated with TPMT enzymatic deficiency; the corresponding gene frequency estimate was 0.024. We also attempted to evaluate the relationship between the molecular TPMT genotype and the reaction to treatments involving thiopurine drugs by analysing a sample of 24 children submitted to curative therapy of acute lymphoblastic leukaemia. Four of them were shown to be heterozygous for the TPMT*3A allele. An examination of their clinical histories showed that all four patients exhibited signs of severe hepatic toxicity during treatment.

Antineoplastic Agents↗
PubMed1999

Two pairs of proven monozygotic twins discordant for familial amyloid neuropathy (FAP) TTR Met 30.

Twin studies are an important tool in medical genetics for the evaluation of the relative roles of genetic and non-genetic factors in several diseases. Familial amyloidotic polyneuropathy type I (FAP-I), TTR Met 30, was present in two sets of proven monozygotic (MZ) twins, one from Majorca and the other from Portugal. Monozygosity was established by analysis of DNA polymorphisms. Both pairs were discordant for age at onset and some clinical manifestations of FAP-I. We reviewed the differences in age at onset and clinical features in both sets and in two other pairs of presumed MZ twins with FAP-I and compared them with those in MZ twin pairs with other Mendelian disorders, such as neurofibromatosis type 1, Huntington's disease, facioscapulohumeral muscular dystrophy, and myotonic dystrophy. We conclude that, in addition to the postulated modifying genes, there must be a significant contribution from non-genetic factors to the phenotypic variability of FAP-I (age at onset and clinical expression), either because of environmental differences or stochastic events during (or after) the twinning process.

Adult↗
PubMed1999

Adenosine deaminase polymorphisms at the protein and DNA levels.

Adenosine deaminase (ADA, E.C. 3.5.4.4) exhibits a well-known polymorphism at the protein level. We have studied ADA and an STR polymorphism exhibiting variation of a TTTA repeat motif at intron 3 of the ADA gene in random samples from northern Portugal (N = 218) and southwestern Germany (N = 114). The ADA phenotype distribution and population data on the worldwide distribution of ADA favor recurrent mutation as an explanation for the maintenance of the ADA*2 gene product at polymorphic frequencies.

Adenosine Deaminase↗
PubMed1998

Conservation of genetic linkage between heat shock protein 100 and glycosylphosphatidylinositol-specific phospholipase C in Trypanosoma brucei and Trypanosoma cruzi.

The experiments described in this paper were designed to try and isolate a recombinant DNA clone encoding a Trypanosoma cruzi homologue of the Trypanosoma brucei glycosylphosphatidylinositol-specific phospholipase C (GPI-PLC) gene. Despite the ready biochemical detection of phospholipase C activities that hydrolyse GPI-anchors of cell surface proteins in T. cruzi, it did not prove possible to isolate any recombinant DNA clones using the T. brucei gpi-plc gene as a probe. On determining the DNA sequence to the 5' side of the gpi-plc gene it was found to be adjacent to a gene that encodes a 100 kDa heat shock protein (HSP100). To investigate whether this linkage between the hspl00 and gpi-plc genes was conserved in T. cruzi, a probe derived from the T. brucei hsp100 gene was used to isolate T. cruzi genomic clones. These were partially sequenced and shown to contain an hsp100 gene. Restriction enzyme fragments located to the 3' side of the T. cruzi hsp100 gene were then sequenced and found to contain a gene that encodes a polypeptide (TcPLC1) that has 46% amino acid sequence identity with the T. brucei GPI-PLC including most of the key residues involved in inositol binding and the catalytic histidine. A recombinant form of TcPLC1 was produced and shown to possess phospholipase C activity towards a GPI-substrate. Thus, the hsp100 and gpi-plc genes are adjacent in T. brucei and this linkage is conserved in T. cruzi. This observation has been used to facilitate the isolation of a clone encoding a T. cruzi phospholipase C gene.

Amino Acid Sequence↗
PubMed1997

Tetra- and pentanucleotide short tandem repeat instability in gastric cancer.

The association between genetic instability in repetitive DNA domains and cancer has been reported in different types of malignancies. In this work we perform a comparative study of 29 gastric tumors with paired normal tissue using seven tetra-(FES/FPS, VWA31/A, HTPO, TH01, MBPB) and pentanucleotide (CD4, TP53) STR polymorphic markers regarding loss of heterozygosity and replication error status. Furthermore, we compare the gene frequencies obtained in normal tissue from patients with those of a normal control population from the same area, looking for allele associations between any of these polymorphic loci and gastric cancer risk. The results have shown that FES/FPS and TP53 present the higher rates of somatic instability. The observed results for TP53 are in accordance with those previously reported in gastric carcinogenesis, while instability of FES/FPS is for the first time reported in this tumor type. Our data suggest that different loci show different rates of instability and/or loss of heterozygosity and do not seem to consist of a result of an RER+ phenotype affecting several genomic repetitive domains. Furthermore, the instability in markers TH01, MBPB, TP53, and FES was generally detected in genotypes involving alleles with a high number of repeats. Comparing gene frequencies in patients and normal controls, no significant differences were found, although longer alleles are consistently more frequent in patients for the markers MBPB, TH01, and CD4.

Alleles↗
PubMed1997

A review of the collaborative exercises on DNA typing of the Spanish and Portuguese ISFH Working Group. International Society for Forensic Haemogenetics.

Since 1992 the Spanish and Portuguese Working Group (GEP) of the International Society for Forensic Haemogenetics (ISFH) has been organizing collaborative exercises on DNA profiling with the aim of making progress on standardization and discussing technical and statistical problems in DNA analysis. A total of four exercises (GEP-92 to GEP-95) have been carried out until now. A consequence of these exercises was the creation of a quality control programme in Spain and Portugal in 1995 which was carried out simultaneously with the GEP-95 exercise. The number of participating laboratories increased from 10 in the first exercise (GEP-92) to 19 in the last exercise (GEP-95). Despite this increasing number of participating laboratories, results remained satisfactory. In the last exercises, all the laboratories used PCR-based DNA polymorphisms with an increasing number of markers obtaining good results. SLPs were used by only 30% of laboratories in the last two exercises but the results indicated a good level of expertise in most of these laboratories. The reasons for these successful results are the common use of the EDNAP protocol for SLP analysis and commercially available kits or common sequenced allelic ladders for PCR-based DNA polymorphisms.

Blood Stains↗
PubMed1997

Analysis of the allelic diversity of a (CA)n repeat polymorphism among alpha 1-antitrypsin gene products from northern Portugal.

The level of molecular heterogeneity associated with alpha 1-antitrypsin gene products was assessed in the population of northern Portugal using three restriction fragment length polymorphisms (RFLPs) corresponding to specific amino acid substitutions and a highly variable (CA)n repeat polymorphism located at the 5' end of the PI gene. The allelic affinities inferred from the analysis of the DNA polymorphisms essentially agree with the evolutionary pattern proposed for the PI gene products on the basis of their amino acid sequences. PI*Z can be considered the most recent common PI allele and was found to be associated with the same predominant haplotype previously reported in northern European populations, thus confirming the hypothesis that most European Z alleles are derived from a single mutation. However, a rare deficient variant that is the likely result of a recurrent Z mutation on an M2 or M4 background was additionally observed. PIS was also found to be associated with a strongly predominant haplotype and seems to be the second most recent PI common allele, while M2 and M3 show weaker associations, suggesting more ancient origins of their corresponding mutations. M1Ala213 and M1Vat213 display more homogeneous (CA)n allele frequency distributions, M1Ala213 representing the most ancient PI allele as inferred from its highest variance in (CA)n allele length.

Alleles↗
PubMed1997

MUC1 gene polymorphism and gastric cancer--an epidemiological study.

Gastric carcinoma is a major cause of cancer death worldwide and, like most human cancers, probably develops after environmental insults acting on normal individuals and/or individuals with increased genetic susceptibility. Mucins are attractive molecules to study the relationship between genetics and environment because they play an important role in the protection of gastric mucosa against environmental insults and exhibit a highly polymorphic genetic variation. We performed a case-control study using Southern blot analysis to evaluate the MUC1 gene polymorphism in a series of blood donors (n = 324) and in patients with gastric carcinoma (n = 159). We found that the distribution of MUC1 alleles is significantly different in the two populations and that small MUC1 alleles and small MUC1 genotypes are significantly more frequent in patients with gastric carcinoma than in controls. Individuals with small MUC1 genotypes are at increased risk for gastric carcinoma development.

ABO Blood-Group System↗
PubMed1997

Characterization of four short tandem repeat loci (THO1, VWA31/A, CD4, and TP53) in northern Portugal.

Allele and genotype frequencies for two tetrameric and two pentameric short tandem repeat (STR) loci (THO1, VWA31/A, CD4, and TP53) were determined in a population sample from northern Portugal. Genotyping of PCR amplification products was done using polyacrylamide gel electrophoresis followed by silver staining; heteroduplex analysis was performed to distinguish THO1 genotypes involving allele 10 and the nonconsensus allele 9.3. For all loci allele frequencies fitted the distribution patterns generally observed in European populations. The observed genotype distributions do not deviate significantly from Hardy-Weinberg expectations, although for VWA31/A a significant excess of heterozygotes involving allele 17 was found. Mother-child pair analyses confirmed the regular Mendelian pattern of inheritance. Because the information content of these systems is high and because their genotyping is technically reliable and simple, CD4, THO1, VWA31/A, and TP53 are appropriate genetic systems for anthropological genetics.

Antigens, CD↗
PubMed1997

MUC6 gene polymorphism in healthy individuals and in gastric cancer patients from northern Portugal.

Mucins exhibit a high degree of genetic polymorphism because of the presence of a variable number of tandem repeats. The aims of this work were to describe the MUC6 gene polymorphism in the Portuguese population and to evaluate whether MUC6 gene polymorphism was involved in individual susceptibility to gastric cancer development, as observed previously for the MUC1 gene. We found that the 10 alleles identified in the population of blood donors (n = 376), by Southern blot analysis, were also found in gastric cancer patients (n = 157). However, significant differences in allelic frequencies between the two populations were observed for 4 of the 10 alleles, in agreement with those described previously for the MUC1 gene; the largest allele was more frequent in blood donors, and smaller alleles were more frequent in gastric cancer patients. Our results suggest that MUC6 gene polymorphism is involved in the predisposition to gastric carcinoma development.

Adult↗
PubMed1996

Cerebrovascular amyloidosis in squirrel monkeys and rhesus monkeys: apolipoprotein E genotype.

Some neuropathological changes characteristic of aging and Alzheimer's disease (AD) in humans are present also in senescent non-human primates. The human apoE4 allele is associated with an increased risk of developing late-onset familial and sporadic AD. We found that rhesus monkeys and three subspecies of squirrel monkeys are homozygous for apoE phenotype with arginine at positions 112 and 158 as in human apoE4. However, in both species threonine replaces arginine at position 61 of human apoE. It was previously shown that arginine 61 was critical in determining apoE4 lipoprotein distribution in humans.

Alzheimer Disease↗
PubMed1996

Failed PCR amplifications of MBP-STR alleles due to polymorphism in the primer annealing region.

The PCR-based STR system MBP-B (myelin basic protein locus B) has been reported to exhibit a high rate of mutations. Using a newly designed pair of primers we present evidence that this is due to failed amplifications caused by a polymorphism in the annealing region of the reverse primer originally designed. With the new reverse primer described here no exclusions were found (out of 59 mother/child pairs analysed) while one was detected with the old set of primers. The results obtained with both pairs of primers in a random population sample (n = 112) from North Portugal are compared. In this sample 13 individuals typed as homozygotes with the pair of primers originally described, were found to be heterozygous when the amplifications were performed with the new reverse primer. By sequence analysis, a substitution in the reverse primer binding sequence originally described was determined. This substitution is located upstream from the repetition site and consists of G-->A transition. This variation reaches polymorphic frequency and is responsible for the relatively frequent null alleles due to failed amplifications when the previously designed primers are used.

Alleles↗
PubMed1995

Specific staining of glycine N-methyltransferase.

Glycine N-methyltransferase from rabbit, human, rat and pig livers was separated by isoelectric focusing and a specific functional staining method was developed through the detection of sarcosine produced from the methylation of glycine. Isozyme patterns obtained in the various species tested differ both in the number of bands and apparent isoelectric points. These differences may explain the contradictory data on the subunit structure and glycosylation status of the enzyme reported so far.

Animals↗